Wireless communication systems, i.e. systems that provide communication services to wireless communication devices such as mobile phones, smartphones etc. (often denoted by UE that is short for user equipment), have evolved during the last decade into systems that must utilize the radio spectrum in the most efficient manner possible. A reason for this is the ever increasing demand for high speed data communication capabilities in terms of, e.g., bitrate and to provide these capabilities at any given time and at any geographical location. This may be obtained by utilizing every available part of the radio frequency interval. Needless to say, this leads to an ever increasing demand for more and more powerful processing capabilities in the wireless communication devices in order to, e.g., schedule the use of the available radio frequency carriers.
Within the third generation partnership project (3GPP) there are currently discussions about increasing requirements on the amount of carriers a UE shall be able to keep track of. At the same time, there is a clear indication that wireless communication system operators are going to operate in radio environments that are characterized by scattered frequency intervals of comparatively small sizes due to the typical situation in many areas where there is a scarceness of available frequencies. As a result of this situation, the networks typically send information to UEs that there are a large number of radio frequency carriers available in the network and which carriers the UE needs to keep track of in order to operate in a satisfactory manner in the network.
For example, in the case of 3GPP long term evolution (LTE) systems (the situation is similar in other types of radio access technology (RAT) systems), a UE shall according to the 3GPP requirements be able to track four LTE frequencies when the UE is operating in in idle and connected mode. However, in the configuration information provided by the network (either through broadcast or dedicated messages), up to eight LTE frequencies can be configured for measurements.
Furthermore, since UEs are capable of handing over between, and operate in, several different RATs, there are discussions within 3GPP to increase even further the minimum number of inter-frequency carriers and cells a UE shall be able to monitor when camping on a radio cell of a universal mobile telecommunications system (UMTS) terrestrial radio access (UTRA) system and when camping on a cell of an evolved UTRA (EUTRA) system. For example, while camped on LTE a UE would need to keep track (i.e. perform regular signal measurements) of more than 20 carriers if configured so by the network (and that is without considering any carriers of a second generation and/or third generation RAT). Although this provides more freedom to a network operator, the network does not know on which of the configured carriers the UE will measure and with which periodicity it will do the measurements.
Consequently, it is quite clear the UEs will be required to measure on more and more carriers when communicating in 3GPP systems, and additionally measure on other radio access technologies such as wireless local area networks (WLAN) and the like. If a UE follows the configurations as discussed above and measures/tracks a large number of carriers when looking for optimal coverage, the UE will use a lot of processing resources and as a result of this quickly drain its battery. Alternatively, in order to not spend processing power on measuring/tracking a multitude of carriers, the UE could be configured to perform such measurements more sparsely, resulting in a scenario where each carrier is “revisited” very seldom with the final consequence of the UE losing contact with the networks altogether. Hence, there is a need for improved ways in which an UE measures carriers in a multi carrier environment.
Patent application publication US2009/0047958 describes methods related to handover between radio cells. Two sets of cells are discussed where signal strengths from the cells are measured with different measurement rates.